1. Field of the Invention
The present invention relates to an electron beam apparatus and an image-forming apparatus, such as a display device, in which the electron beam apparatus is employed.
2. Related Background Art
Heretofore, two types of electron-emitting devices are known; i.e., a thermal electron source and a cold cathode electron source. Cold cathode electron sources include electron-emitting devices of field emission type (hereinafter abbreviated to FE type), metal/insulating layer/metal type (hereinafter abbreviated to MIM type), and surface conduction type (hereinafter abbreviated to SCE), etc.
Examples of FE type devices are described in, e.g., W. P. Dyke and W. W. Dolan, xe2x80x9cField emissionxe2x80x9d, Advance in Electron Physics, 8, 89 (1956) and C. A. Spindt, xe2x80x9cPHYSICAL Properties of thin-film field emission cathodes with molybdenium conesxe2x80x9d, J. Appl. Phys., 47, 5248 (1976).
One example of MIM type devices is described in, e.g., C. A. Mead, xe2x80x9cThe tunnel-emission amplifierxe2x80x9d, J. Appl. Phys., 32, 646 (1961).
One example of surface conduction electron-emitting devices is described in, e.g., M. I. Elinson, Radio Eng. Electron Phys., 10, (1965).
A surface conduction electron-emitting device utilizes a phenomenon that when a thin film having a small area is formed on a substrate and a current is supplied to flow parallel to the film surface, electrons are emitted therefrom. As to such a surface conduction electron-emitting device, there have been reported, for example, one using a thin film of SnO2 by Elinson as cited above, one using an Au thin film (G. Ditter: xe2x80x9cThin Solid Filmsxe2x80x9d, 9, 317 (1972)), one using a thin film of In2O3/SnO2 (M. Hartwell and C. G. Fonstad: xe2x80x9cIEEE Trans. ED Conf.xe2x80x9d, 519 (1975)), and one using a carbon thin film (Hisashi Araki et. al.: xe2x80x9cVacuumxe2x80x9d, Vol. 26, No. 1, p. 22 (1983)).
As a typical configuration of those surface conduction electron-emitting devices, FIG. 25 shows the device configuration proposed by M. Hartwell in the above-cited paper. In FIG. 25, denoted by reference numeral 1 is an insulating substrate. 2 is a thin film for forming an electron-emitting region which comprises, e.g., a metal oxide thin film formed by sputtering into an H-shaped pattern. An electron-emitting region 3 is formed by the energizing process, i.e. flowing an electrical current, called forming (described later). 4 will be here referred to as a thin film including the electron-emitting region. The dimensions indicated by L1 and W in the drawing are set to 0.5-1 mm and 0.1 mm, respectively. The electron-emitting region 3 is shown schematically because its position and shape are not certain.
In those surface conduction electron-emitting devices, it has heretofore been common that the electron-emitting region forming thin film 2 is subjected to the energizing process called forming in advance to form the electron-emitting region 3 before starting emission of electrons. The term xe2x80x9cformingxe2x80x9d means the process of applying a DC voltage or a voltage rising very slowly at a rate of, for example, 1 V/minute, across the electron-emitting region forming thin film 2 to locally destroy, deform or denature it to thereby form the electron-emitting region 3 which has been transformed into an electrically high-resistance state. The electron-emitting region 3 emits electrons from the vicinity of a crack generated in a portion of the electron-emitting region forming thin film 2.
The electron-emitting region forming thin film 2 including the electron-emitting region 3 which has been formed by the forming process will be here referred to as the thin film 4 including electron-emitting region. In the surface conduction electron-emitting device after the forming process, a voltage is applied to the electron-emitting region including thin film 4 to supply the device with a current, whereupon electrons are emitted from the electron-emitting region 3.
The above surface conduction electron-emitting device is simple in structure and easy to manufacture, and hence has an advantage that a number of devices can be formed into an array having a large area. Therefore, various applications making use of such an advantage have been studied. Examples of the applications are an electron beam apparatus, e.g., a charged beam source and an electron beam machining apparatus, and a display device.
As an example in which a number of surface conduction electron-emitting devices are formed into an array, there is an electron source wherein surface conduction electron-emitting devices are arranged in parallel, both ends of the devices are interconnected by respective leads to form one row of an array, and a number of rows are arranged to form, the array. (See, e.g., Japanese Patent Application Laid-Open No. 64-31332). In the field of image-forming apparatus such as image display devices, particularly, flat type display devices using liquid crystals have recently become popular instead of CRTs, but they are not of an emission type and have a problem of requiring backlights or the like. Development of self-luminous display devices have therefore been desired. An image-forming apparatus in which an electron source having an array of numerous surface conduction electron-emitting devices and a fluorescent substance radiating visible light upon impingement of electrons emitted from the electron source are combined with each other to form a display device, is a self-luminous one which is relatively easy to manufacture and has good display quality while giving a large screen size. (See, e.g., U.S. Pat. No. 5,066,883).
In the conventional electron source comprising numerous surface conduction electron-emitting devices, a desired one of the devices, which is to emit electrons for causing the fluorescent substance to radiate light, is selected by combination of wirings (referred to as row-direction wirings) which interconnect both ends of the numerous surface conduction electron-emitting devices arranged in parallel, control electrodes (called grids) which are disposed in a space between the electron source and the fluorescent substance to lie in a direction (called a column direction) perpendicular to the row-direction wirings, and an appropriate drive signal applied to the row-direction wirings and the grids. (See, e.g., Japanese Patent Application Laid-Open No. 1-283749).
The electron-emitting devices are handled under a vacuum, but details of an electron-emitting characteristic of the surface conduction electron-emitting device under a vacuum are yet scarcely clear.
A description will now be made of problems caused in the conventional surface conduction electron-emitting devices as described above and the image-forming apparatus, etc. employing those devices.
Problem 1
If the conventional electron-emitting device is left not driven in an image-forming apparatus or an enclosure for maintaining a vacuum therein, an electrical characteristic (current-voltage) of the electron-emitting device is changed and an emission current from the device is increased temporarily. A change rate of the emission current depends on the period of time during which the device is left not driven (i.e., standing time), the vacuum atmosphere (degree of vacuum and kinds of residual gases), the driving voltage and so on.
Problem 2
In the conventional electron-emitting device, if a pulse width of the voltage applied to the device is changed, an emission current is varied and, therefore, it is difficult to control the amount of electrons emitted with the pulse width.
Problem 3
In the conventional electron-emitting device, if a value of the voltage applied to the device is changed, its electrical characteristic is varied and an emission current is also varied correspondingly. It is therefore difficult to control the amount of electrons emitted with the voltage value.
Problem 4
When the conventional electron-emitting devices having Problem 1 is employed in an image-forming apparatus, contrast and sharpness of the formed image are lowered because of a change in the intensity of electron beam. Particularly, when the formed image is a fluorescent image, brightness and color of the fluorescent image are varied.
Problem 5
When the conventional electron-emitting devices having Problems 2 and 3 are employed in an image-forming apparatus, a difficulty in control of the intensity of electron beam with the voltage or the pulse width thereof applied to the device makes it difficult to achieve gradation control of the formed image. Particularly, when the formed image is a fluorescent image, it is difficult to control brightness and color of the fluorescent image.
In view of the problems as described above, an object of the present invention is to provide an electron-emitting device and an electron beam generator in which an emission current is stable with a very small change in the amount of electrons emitted depending on the period of time during which the device is left not driven (i.e., standing time) and the vacuum atmosphere. Another object of the present invention is to provide an image-forming apparatus which can produce a sharp image with high contrast, in particular, an image-forming apparatus which can form a luminous image with a small change in brightness. Still another object of the present invention is to provide an image-forming apparatus in which it is easy to carry out gradation control, in particular, an image-forming apparatus which is easy to control brightness and color of a luminous image.
The above objects are achieved by the present invention summarized below.
With one aspect of the invention, there is provided an electron beam apparatus comprising an enclosure in which an electron-emitting device having an electron-emitting region between opposite electrodes is disposed, wherein the electron-emitting device exhibits a characteristic such that an emission current is uniquely determined with respect to a device voltage.
With another aspect of the invention, there is provided an electron beam apparatus comprising an enclosure in which an electron-emitting device having an electron-emitting region between opposite electrodes is disposed, wherein the interior of the enclosure is maintained under an atmosphere effective to prevent structural changes of the electron-emitting device.
With still another aspect of the invention, there is provided an image-forming apparatus comprising an enclosure in which an electron source and an image-forming member are disposed, the apparatus producing an image in response to an input signal, wherein the electron source comprises an electron-emitting device having an electron-emitting region between opposite electrodes, the electron-emitting device exhibiting a characteristic such that an emission current is uniquely determined with respect to a device voltage.
With yet another aspect of the invention, there is provided an image-forming apparatus comprising an enclosure in which an electron source and an image-forming member are disposed, the apparatus producing an image in response to an input signal, wherein the electron source comprises an electron-emitting device having an electron-emitting region between opposite electrodes, and the interior of the enclosure is maintained under an atmosphere effective to prevent structural changes of the electron-emitting device.